The Bayer process is the most common process used to produce alumina (Al2O3) from bauxite ore. Alumina producers are constantly striving to make the Bayer process more economical; producers want to be able to make as much alumina as possible at the lowest operating costs. One aspect of the Bayer process that directly impacts process economics is the production of and the transfer of slurry. Specifically, the transfer of bauxite and red mud containing slurries are problematic.
Bauxite containing slurries are formed when bauxite is mixed with liquid, such as the spent liquor. Depending upon bauxite hardness and particle size, a grinding stage may be necessary to form transferable slurry, for example pumpable slurry. Ball mills, rod mills, or combined rod and ball mills may be used to wet grind the bauxite so that slurry can be made. Once this slurry is formed it then needs to be transferred to other stages of the Bayer process, one of which is a critical stage, the digestion stage, which involves the extraction of alumina from bauxite containing slurry.
Red mud slurries contain red mud and Bayer process liquor. This type of slurry, for example, needs to be transferred from the red mud settler to the red mud washers.
Various apparatuses, for example one or more pumps, are used to transfer slurry from one point in the Bayer process to another. Problems with slurry throughput can occur through these apparatuses. Specifically, the rate of transfer through pumps and other apparatuses may be slower than design. For example, in one Bayer process plant, some pumps were found to be capable of only transferring 60% of their design flow.
Gravimetric forces also play a role in the transfer of slurry of one point in the Bayer process to another.
Improvements in the efficiency of slurry transfer in a Bayer process are addressed in this disclosure.